1. Field of the Invention
The present invention relates to a filter for filtering a particle-containing medium and of the type including a chamber having a first section and a second section, a substantially horizontally extending partition plate which separates the two sections, the partition plate carrying a plurality of filter devices through which the medium to be filtered passes from the first section to the second section, and a plurality of nozzles connected with a source of pressurized cleaning fluid and adapted to generate a flow of cleaning fluid directed toward the partition plate and/or the filter devices. The nozzles include a housing having a inlet opening and an outlet opening for the cleaning fluid, the openings formal between them a passage defined by a wall, a valve body having a valve head and a valve rod, the valve rod being arranged to be moved in the interior of the passage between a first end position to control the flow of the cleaning fluid toward the partition plate and/or the filter devices, the outlet opening forming a valve seat adapted to cooperate with the valve head in the first position to prevent outflow of the cleaning fluid, a means for generating a bias of the valve body in a direction toward the first position.
2. The Prior Art
Filters having such cleaning nozzles, by means of which cleaning of the filter devices may be performed, have acquired great interest among the users, because when ejecting a cleaning medium for the cleaning nozzles it is possible to perform regular cleaning of the filter devices, which may, e.g., be formed by vertically suspended bag filters, on site, i.e., without it being necessary to remove the filter devices from the filter chamber itself. According to the conventional use of such filters, one or more vertically hanging bag filters are secured to the partition plate, and the first section in the chamber forms a lower dust-laden area, while the second section forms an upper clean air area. Filtering takes place in that the particle-containing medium, which may typically be air, is passed into the first section of the chamber, through the filtering wall of the bag filters, and further up through a hole in the partition plate and into the second section. The cleaning nozzle, which is mounted in the partition plate, and which is adapted to generate a flow of cleaning fluid toward the bag filters, is provided with a cleaning fluid under pressure via a supply line. An example of this is described in European Patent Application No. 719 577, where the nozzles comprise a movable valve body having a valve head and a valve rod. The rod is kept closed by means of a spring which tries to keep the valve head engaged with a valve seat. The nozzle opens when the pressure of the cleaning fluid directly against the upper side of the valve head exceeds the oppositely directed force of the spring, thereby allowing the cleaning fluid to flow out in a direction perpendicular to the longitudinal axis of the valve rod, after the flow has been deflected by the upper side of the valve head. Because of this structure, variations in the pressure of the cleaning fluid will only give rise to relatively modest changes in the position of the valve head. During the cleaning process, the cleaning fluid can moreover only be ejected substantially horizontally along the underside of the partition plate and toward the adjoining bag filter, following which the cleaning fluid runs down the bag filter by gravity. Thus, there is no flushing proper of a large area of the upper part of the bag filter in which large amounts of particles often settle, and the cleaning therefore does not have an optimum efficiency.
The principle of the nozzle known from the above-mentioned European patent application is shown more fully in FIG. 1 of the present application. In practice, it has been found inexpedient with this known nozzle that only a very small gap is formed between the valve head and the valve seat in use, as small particles contained in the cleaning fluid can settle on the valve head, as indicated by reference numeral 100. Such small particles have the effect that the nozzle cannot close tightly when the flow of the cleaning fluid stops, and the cleaning nozzle must therefore be removed from the filter at regular intervals to be cleaned. This leakage means in certain circumstances that, in the normal operation of the filter, the particle-containing medium to be filtered flows into and possibly settle inside the nozzle, which must be avoided particularly when the specifications of use of the filter demand that no hotbed of bacterial growth must be present anywhere in the filter, as is the case in, e.g., sanitary systems or in the food industry.
The present invention is intended to remedy to the above-mentioned inexpediencies by providing a filter by means of which a completely tight engagement of the valve head with the valve seat in the closed state of the nozzle can be achieved to a greater degree than before, and by means of which it can be possible also to obtain a more effective cleaning of the filter devices, if desired. This is achieved according to the invention in that the valve body also includes a piston device acting as a hydraulic piston, the piston device being arranged between the inlet opening and the outlet opening and adapted to generate a pressure loss in the cleaning fluid during its flow from the inlet opening and trough the passage, whereby the valve body is moved in a direction toward the second position of the cleaning liquid through the outlet opening.
The pressure of the cleaning fluid is hereby used to open the valve body, the pressure being applied to the piston device to act in a direction against the spring force. The nozzle is hereby more sensitive to variations in the pressure of the cleaning fluid, which is utilized according to the invention to allow setting of the valve body in various cleaning positions, according to which part of the bag filter is to be cleaned. Moreover, it is hereby possible to generate a very large opening of the nozzle, as needed, so that particles, if any, of the size conventionally found in the cleaning fluid, also as a consequence of recirculation of the cleaning fluid, can escape through the gap between the valve seat and the valve head.
In expedient embodiments, the piston device may be constructed as a cylindrical body having plurality of small channels therethrough so that the cleaning fluid is driven through the plurality of small channels, which give rise to a relatively great pressure drop. As mentioned, this pressure drop creates a force on the piston rod which tries to move the piston rod in a direction against the spring force and thus causes opening of the nozzle. With particular constructional advantages, the channels may be constructed as depressions in the peripheral face of the cylindrical body, and the channels may preferably be constructed helical depressions so that the cleaning fluid is given a helical motion which may be utilized for creating an expedient ejection pattern. When also providing the passage with a constriction in combination with helical channels, a good distribution of the cleaning fluid is achieved. Particularly advantageously, the nozzles of the filter may be constructed so that in various positions between the first and second end positions the valve body may generate pre-defined outflow patterns for the cleaning fluid. Particularly, it will hereby be possible selectively to perform cleaning of the partition plate or of the bag filter. This may preferably take place in that the surface of the valve head facing the outlet opening has a conically tapering part with a cone angle v1, which is preferably very small, whereby the cleaning fluid, is a given position of the valve body, will be reflected upwards and hit the partition plate.